The present invention relates to a process for the removal of hydrogen sulfide contained in natural gas.
More specifically, the present invention relates to a process for the reduction of the hydrogen sulfide contained in natural gas to concentrations lower than 1% molar.
It is known that natural gas has now become a source of thermal energy which represents one of the main alternatives to traditional fuels of a fossil nature, in particular to the fuel oils of petroleum origin, which are considered as being one of the main causes of the greenhouse effect which influences the earth's climate.
Natural gas, coming from production fields, mainly consists of methane but can also contain, in addition to significant traces of higher C2–C7+ hydrocarbons, variable quantities of inert or polluting gases, for example, carbon dioxide or H2S, whose presence must be eliminated or reduced in order to meet the specifications for use.
Said specifications include respecting the Wobbe index, a parameter defined by the ratio between the thermal value (upper or lower) of gas and its density with respect to air, as well as the a H2S content which must be practically null.
Methods for the removal of inert or polluting gases from natural gas, nitrogen or hydrogen sulfide in particular, are known in scientific literature. Most of these processes, however, are essentially based on cryogenic removal, as in the case of nitrogen, or on removal by absorption with alkyl amines, as in the case of hydrogen sulfide, with generally efficacious but uneconomic results. In particular, there are natural gas fields where the concentration of hydrogen sulfide is so high that their exploitation is not convenient from an economic point of view, due to the high costs for the separation and treatment of the polluting product (H2S). Particularly relevant is the treatment step of hydrogen sulfide which, after separation, is transformed to elemental sulfur, with consequent disposal problems.
A process for the removal of hydrogen sulfide from natural gas has now been found by the Applicant, which allows the polluting product to be recovered at a pressure substantially equal to that of the production of natural gas, making it therefore possible to introduce the polluting product itself back to the production field. In this way, all problems associated with transforming the hydrogen sulfide into sulfur and with the disposal of the latter, are completely eliminated.